DESCRIPTION (adapted from application): The Field Operations Core (FOC) will provide field logistics and technical personnel support to perform the 4 respective Project efforts. Members of this Core will work closely with investigators from each of the respective Projects to collect the data, samples, and specimens needed to achieve the study objectives. In this manner, the Field Operations Core will serve as a critical resource for efficient and coordinated data collection for the 4 research efforts within the Program Project. The Field Operations Core has 3 primary responsibilities: (1) recruitment, enrollment and maintenance of the respective study cohorts; (2) documentation of the subjects' health, residential and activity status; and (3) collection of biological samples for subsequent laboratory analysis and characterization.